I'm sharing same Apple ID on iPad and iPhone, how can I change it from iPad?

What exactly do you want to change ? If you want to change the account's details (e.g. primary email address) then tap on it in Settings > iTunes & App Store and tap 'view apple id' on the popup and log into the account (you might then need to log out and back into the account on your phone so as to pick the account's new id on it) ; to log out of an account, tap on it in Settings > iTunes & App Store and tap 'sign out' on the popup (you will need to do the same on the phone to log out of the account on it). To logout of icloud on a device : Settings > iCloud > Sign Out